A guide wire is used to guide a catheter which is used in the treatment of a portion on which it is difficult to perform surgery, in minimal invasive treatment for a human body, in cardioangiographic examination, or the like. When percutaneous coronary intervention (PCI) or the like is performed, a guide wire along with a balloon catheter under X-ray fluoroscopy is inserted into the vicinity of a stenotic portion of a coronary artery, that is, a target portion, while a distal end of the guide wire protrudes further than a distal end of the balloon catheter, and a distal end portion of the balloon catheter is guided to the vicinity of a stenosis.
JP-A-10-146390 discloses a guide wire that is used in this type of treatment. This guide wire is configured to include a wire main body (core member) that has flexibility; a coil (X-ray imaging metal coil) that is installed so as to cover an outer circumference of a distal end portion of the wire main body, and is made by winding a wire rod with a semicircular cross section; and coating layers (coating member made of synthetic resin, and a hydrophilic lubricating layer) that cover the outermost surfaces of the wire main body and the coil.
When the guide wire disclosed in JP-A-10-146390 is operated as described above, phenomena to be described hereinbelow may occur depending on a state of the coronary artery, for example, the degree of curving.
When the coil of the guide wire reaches (is inserted into) a steeply curved portion of the coronary artery, if the guide wire is pushed, an excessive force (which causes plastic deformation of the coil) is applied to the coil. In this case, a portion of the wire of the coil moves upward relative to the adjacent wire, and the coil undergoes plastic deformation. Since the wire rod of the coil has a semicircular cross section, a corner of the wire rod is stuck to the adjacent wire rod. For this reason, the coil does not return to a typical (normal) state, and a pushing force is not reliably transmitted to the distal end portion of the wire main body from a proximal end portion of the wire main body via the coil, that is, pushing performance is considerably decreased.
In a case where the plastic deformation of the coil occurs, the guide wire bulges (the outer diameter increases) due to the plastic deformation, and thus even the hydrophilic lubricating layer is provided on the coil of the guide wire that is disclosed in JP-A-10-146390; the catheter cannot be inserted due to the thickness of the guide wire.
In addition, in a case where the guide wire bulges as described above, when the coil of the guide wire reaches (is inserted into) the steeply curved portion of the coronary artery or the like, relatively large friction resistance may occur between the hydrophilic lubricating layer and the curved portion. For this reason, torque may not be reliably transmitted to the distal end portion of the wire main body from the proximal end portion of the wire main body via the coil, that is, torque transmission performance is considerably decreased, and the coil is ruptured due to an increase in the friction resistance.